1. Field of the Invention
The present invention relates generally to apparatus for transporting individual or continuous sheets of web material, and more particularly to apparatus for transporting a web by pulling its leading end portion. While the invention has various types of applications, one particular application of the invention is to machines for processing a photosensitive web of film or print paper by drawing the web through successive developing, fixing, washing and other web-treating sections in the processor.
2. Description of the Prior Art
In photofinishing operations, it is common to move continuous or individual sheets of photosensitive web material, such as film or print paper, through a number of baths and drying sections in a processor. If this is to be done efficiently, it is necessary that a quick method of threading the web through the processor be available. Known devices have used an endless belt which is trained around a plurality of rollers, often in a sinuous path, to transport the web through the various processing sections. Typically, a leading portion of the web is secured to the transport belt at an entrance end of the processor to initiate feed-through of the entire web. Attachment of the web to the transport belt can be accomplished with a coupling bar such as disclosed in U.S. Pat. No. 2,878,924, granted Mar. 24, 1959. In operation, the leading portion of the web is first secured to the coupling bar. This may be done, for example, by passing the leading portion through a slot in one end of the bar and winding the leading portion several times around the bar to prevent their separation, as disclosed in U.S. Pat. No. 3,810,568, granted May 14, 1974. Then, an opposite end of the coupling bar is attached to the transport belt. This generally is accomplished by pinching a longitudinal section of the belt across its width to make the belt section narrow enough to fit between oppositely spaced gripper members of the coupling bar. When the belt is released between the gripper members (which are spaced apart a distance slightly less than the belt width) the belt section strives to return to its normally flat condition; whereupon, the respective longitudinal edges of the belt are frictionally held by the gripper members to attach the coupling bar to the transport belt.
Once the coupling bar is attached to the transport belt, movement of the belt around the rollers draws the web through the processor from its entrance end. At an exit end of the processor, the coupling bar is removed from the transport belt and the leading portion of the web is wound onto a take-up spool.
While the method taught by the prior art of pinching the belt across its width to connect the belt and the coupling bar may be successfully employed, it will be observed that this method suffers from several disadvantages. For example, an operator must stop the belt to transversely pinch it or else experience some difficulty in handling the moving belt, especially when it has been wetted by the processing solutions. Moreover, the plastic material commonly used in construction the belt may become less flexible in time, further making it difficult to manually pinch the belt across its width for insertion between the gripper members of the coupling bar.
Alternatively, mechanical means may be used to transversely pinch the moving belt. For example, as disclosed in U.S. Pat. No. 3,713,649, granted Jan. 30, 1973, a beltwarping block, through which successive sections of a moving belt are continuously advanced, bows the belt sections across their respective widths to make them fit between the gripper members of a coupling bar. However, while such mechanical means may be used, it tends to impede movement of the belt and may possibly wear the belt down or tear it.